Aqueous crumb rubber composition

ABSTRACT

A fluid or semifluid additive composition useful for asphalt paving comprises between about 10% and about 50% crumb rubber, about 10% and about 50% petroleum hydrocarbon having at least about 50% aromatics, between about 10% and about 50% surface active clay, and water, by weight.

RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.09/989,763, filed Nov. 19, 2001 now U.S. Pat. No. 6,653,389, whichclaims priority to provisional application serial No. 60/252,351, filedon Nov. 20, 2000, and provisional application serial No. 60/270,096,filed on Feb. 20, 2001.

BACKGROUND OF THE INVENTION

U.S. Pat. Nos. 5,539,029 and 5,811,477 disclose aqueous asphalt emulsioncompositions containing rubber particles and polymer latex in specificratios and methods for preparing and using the rubber-containing asphaltemulsions. The methods of preparing the emulsions are advantageous overprevious methods of mixing rubber particles with asphalt at temperaturesabove 300° F., and typically between about 350° F. and 500° F. Such hightemperature mixing is environmentally disadvantageous, especially whenair pollution standards are violated.

SUMMARY OF THE INVENTION

Aqueous rubber-containing additive compositions may be used forimproving asphalt compositions including recycled asphaltic concrete(RAP) and other asphalt paving and road surface compositions. Theaqueous rubber-containing compositions of the present invention arefluid or semifluid additives comprising and preferably consistingessentially of a mixture of crumb rubber, aromatic petroleumhydrocarbon, surface active clay and/or rheological or thixotropicagent, and sufficient water to form the fluid or semifluid composition.The aromatic hydrocarbon and crumb rubber may be added to a mixture ofwater and clay and/or rheological agent, or the crumb rubber added to anaqueous emulsion of the aromatic hydrocarbon and a thixotropic agent.The additive is prepared at substantially ambient temperatures ortemperatures below the boiling point of the liquid composition. Thecomposition may also contain polymer latex. Other materials may bepresent in a final additive composition, as will be disclosed furtherhereinafter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The additive composition of the present invention is convenientlyprepared by mixing the ingredients at substantially ambient temperature,e.g., a temperature between about 35° F. and about 110° F., and morepreferably between about 60° F. and about 95° F., or at highertemperatures, if desired, but below the boiling point of the aqueouscomposition. Since a substantial advantage is realized by not having toheat the materials prior to or during mixing, it is most advantageous tosimply mix the ingredients at the temperature of the environment at thetime and place of mixing. Such ambient temperature mixing avoids thenecessity of heating equipment and use of heating fuel or energy, thusfurther improving the efficiency and reducing costs. However, undercertain conditions, for example in cold weather, heating may be appliedso long as the composition temperature is below its boiling point.

A preferred composition of the invention is a fluid or semifluidadditive composition containing crumb rubber, aromatic petroleumhydrocarbon, clay and/or other rheological agent, and water. The aboveamounts as well as those expressed hereinafter are given by weight.

The clays used in the additive compositions of the invention arepreferably the surface active clays, i.e., a clay which has wettingproperties thus reducing the surface tension between the components inan aqueous mixture. The preferred surface active clays are capable ofmaintaining suspension of the crumb rubber in the mixture aqueouswithout settling, as well as substantially preventing separation of theliquid aromatic hydrocarbon in the water-containing mixture. Examples ofuseful surface active clays include the bentonites, sodium bentonite orsodium montmorillonite, as well as calcium bentonite. For some additivemixtures, it is preferred to use non- or low-swelling or low-expandingclays such as calcium bentonite and kaolin. Other useful clays includehydrated aluminum silicate and hydrated magnesium silicate clays such asserpentine, chrysotile, asbestos, talc, and hydrated aluminum-magnesiumsilicates such as attapulgite and fuller's earth. The above clays aregiven by way of example, and other clays, known to those skilled in theart, may be used. Mixtures of such clays may also be used.

Rheological agents, also referred to as thixotropic agents or thickenersmay be used in addition to or instead of the aforesaid clays. Suchagents, include urethanes, alkali swellable latex thickeners such as SBRand acrylic latexes, cellulose products, gums, starch products, alkylamines, polyacrylic resins, and polymer fibers. Useful polymer fiberscomprise natural, synthetic or semisynthetic fibers. Natural fibersinclude polysaccharides such as starch, cellulose, pectin, seaweed andvegetable gums. Synthetic fibers include thermoplastic and thermosettingsynthetic resins. Thermoplastic polymers include nylon, PVC,polyethylene, polystyrene, polypropylene, fluorocarbons, polyurethaneand acrylic resins (acrylates). Thermosetting resins includecross-linked polyethylene, phenolics, alkyd and polyester resins. Thesemisynthetic polymer resin fibers are cellulosics including rayon,methylcellulose, cellulose acetate and modified starches. Any polymerfibers of the aforesaid type may be used. Preferred fibers aresemisynthetic polymer fibers obtained from recycled materials such asused newsprint or other paper, cardboard, processed wood or similarprocessed cellulosic fiber materials. Useful fibers may be obtained fromother recycle sources including ground up rubber tires which includetire carcass fibers such as nylon, polyester and rayon fibers. If used,fibers present in the solids mix may be in a rubber particle:polymerfiber ratio of between 1:99 and 99:1, respectively, by weight, althoughthe amount of fibers is preferably between about 0.1% and about 10%, byweight of the solids mix. Such useful rheological agents and others aredisclosed in U.S. Pat. No. 5,811,477, the description of which isincorporated herein by reference.

The crumb rubber used in the additive composition of the inventioncomprises rubber particles. Any rubber particle sizes may be used.However, preferably at least a portion of the particles will pass a #10mesh U.S. series sieve, and more preferably passing a #20, #30 or #40mesh sieve and up to #200 mesh. The rubber particles may be natural,thermoplastic or synthetic rubber or mixtures of the rubbers. Examplesof synthetic rubbers are polysulfides, polychloroprene,butadiene-styrene copolymers (SBR), polyisoprene, butyl rubber(isobutylene-isoprene copolymers), polyacrylonitrile, polyurethane,silicone and nitrile (acrylonitrile-butadiene copolymers). Thermoplasticrubbers include block copolymers of styrene-butadiene or styreneisoprene. The rubber may be obtained from recycled or reclaimed rubbertire products. Such particles are produced by grinding used rubber tiresto relatively small particle sizes. The recovery and use of such crumbrubber particles are more fully described in U.S. Pat. No. 5,811,477,the description of which is incorporated herein by reference. The rubberparticles need not be from used rubber sources and any portion or all ofthe rubber may be virgin.

The aromatic petroleum hydrocarbon is one having above about 50%,preferably above about 55% and more preferably above about 65%aromatics, by weight. Such materials are specifically disclosed in U.S.Pat. No. 4,298,397, the description of which is incorporated herein byreference. These aromatic hydrocarbons used may comprise mixtures ofsuch hydrocarbons. Preferred aromatic hydrocarbons have initial boilingpoints above about 500° F. An example of commercially available aromatichydrocarbon composition is Dutrex®, available from Shell Chemical Co.

The aromatic hydrocarbon used in the composition may also bepolymer-modified, preferably where no polymer latex is present in thecomposition. Polymers used for modifying the hydrocarbon are syntheticpolymers, which have been added to or mixed with the liquid hydrocarbonand are well known to those skilled in the art. Preferred syntheticpolymers are a styrene-butadiene copolymer such as SBR orstyrene-butadiene-styrene block copolymers sold under the registeredtrademarks Kraton® or Hytrel®. The SBR may also be cross-linked, forexample, with carboxylate groups resulting from treatment withmethacrylic acid, or the like. Other useful polymers include neoprene,acrylic, vinylacrylic, acrylic terpolymers, nitrile, polyvinyl alcohol,polyvinyl acetate, vinyl acetate-ethylene, vinyl ester copolymers,ethylene vinyl chloride, polyvinylidene chloride, butyl,acrylonitrile-butadiene, polyurethanes, silicones, and block copolymerssuch as styrene-isoprene (SIS), styrene-ethylene-vinyl acetate (SEVAS)and styrene acrylate. The amount of polymer present in the aromatichydrocarbon may be up to about 20% by weight of the hydrocarbon presentin the composition.

The composition of the invention also optionally includes polymer latexor latex rubber. Such latexes are disclosed in U.S. Pat. No. 5,811,477,the description of which is incorporated by reference. Where latex isused, preferred amounts are between about 1% and about 10%, by weight,of the additive composition.

The additive composition of the invention may be prepared by a number ofdifferent methods. For example, water and a surface active clay may bemixed to form a slurry composition, and the crumb rubber and aromaticpetroleum hydrocarbon blended with the slurry. The crumb rubber andaromatic hydrocarbon may be separately added to the aqueous slurry, orthey may be pre-mixed with the mixture blended with the slurry. Theamount of water used in preparing the composition is sufficient to forma fluid or semifluid composition capable of being poured or pumped.

An alternative method of preparing the additive is to first prepare anaqueous emulsion of the aromatic petroleum hydrocarbon and mix the crumbrubber and a clay or rheological agent or mixtures of the agent and claywith the aqueous emulsion. For this method, with an emulsifier presentin the aqueous emulsion, the clay used need not be a surface active clayif the aqueous emulsion contains enough emulsifier to maintain the crumbrubber in colloidal dispersion or suspension in the additivecomposition. The aqueous emulsion may be anionic, cationic or non-ionicwith specific emulsifiers used for preparing such emulsions well knownto those skilled in the art, such as disclosed in U.S. Pat. No.4,298,397, the descriptions of which are incorporated herein byreference.

The amounts of crumb rubber and aromatic petroleum hydrocarbon arebetween about 10% and about 50%, by weight of the additive composition,respectively. The amount of clay and/or rheological agent may be betweenabout 0.1% and about 50%, by weight. Where clay is used as therheological agent, alone or as a major amount of the rheological agent,e.g., above about 50%, the amount used in the additive composition ispreferably between about 1% and about 50% and more preferably betweenabout 10% and about 50%, by weight, of the additive composition. Whencellulosic fibers such as methylcellulose or other cellulose-containingor derived fiber materials are used as the rheological agent, smalleramounts such as about 0.1% up to about 20% may be used. Other of theaforesaid rheological agents are preferably used in amounts of betweenabout 1% and about 25%. The specific ratios of the ingredients willdepend on the use of the additive and the type of product to which it isadded.

The aqueous additive composition of the present invention is especiallyuseful for mixing with asphalts, particularly asphalt/aggregate mixturesused for road surfacing or paving. The use and advantages of crumbrubber in asphaltic paving compositions is well known in the asphaltpaving art. The compositions of the present invention are especiallyadvantageous since the petroleum aromatic hydrocarbon seasons the rubberin-situ in the aqueous composition at ambient or environmentaltemperatures. The presence of the aromatic hydrocarbon within theaqueous fluid composition gradually softens the rubber, making ittackier, more pliable and readily blended with liquid asphalt. Theadditive compositions may be used in hot mix, warm mix or cold mixasphalt processing, all well known to those skilled in the art. Theamount of additive used in such processing will depend on therequirements as well as the types of asphalts and asphaltic compositionsused in the hot, cold or warm mix processing. Typical amounts will bebetween about 5% to about 50%, by weight, of the asphalt. The additivecomposition is also especially useful in treating RAP, recycledasphaltic concrete paving compositions. Such RAP processing may beaccomplished using the additive composition of the invention with 100%RAP or mixtures of RAP and virgin asphalt/aggregate blends. These aswell as other uses and advantages of the compositions of the inventionwill be evident to those skilled in the art.

What is claimed is:
 1. A method of preparing a fluid or semifluidadditive composition comprising: mixing water and an ingredient selectedfrom the group consisting of clay and rheological agent to form a slurrycomposition, and mixing crumb rubber and an aromatic petroleumhydrocarbon having above about 50% aromatics, by weight, with saidslurry composition to form a fluid or semifluid additive compositionthat comprises water, between about 10% and about 50% by weight clay,between about 10% and about 50% by weight aromatic petroleumhydrocarbon, and between about 10% and about 50% by weight crumb rubber.2. The method of claim 1 wherein said clay is a low expanding ornon-expansive surface active clay.
 3. The method of claim 1 wherein saidcrumb rubber comprises particles of reclaimed rubber, at least a portionof which pass through a #10 mesh U.S. series sieve.
 4. The method ofclaim 1 wherein said crumb rubber comprises particles of reclaimedrubber, at least a portion of which pass through a #200 mesh U.S. seriessieve.
 5. The method of claim 1 wherein said aromatic petroleumhydrocarbon is polymer modified and contains up to about 20%, by weight,synthetic polymer.
 6. The method of claim 1 wherein said crumb rubberand said aromatic petroleum hydrocarbon are mixed with said slurrycomposition at substantially ambient temperature.
 7. The method of claim1 wherein said crumb rubber and said aromatic petroleum hydrocarbon aremixed with said slurry composition at a temperature below the boilingpoint of said slurry composition.
 8. A method of preparing an additivecomposition comprising mixing an aqueous emulsion of an aromaticpetroleum hydrocarbon having above about 50% by weight aromatics withcrumb rubber and an ingredient selected from the group consisting ofsurface active clay and rheological agent, to form a fluid or semifluidadditive composition that comprises water, between about 10% and about50% by weight aromatic petroleum hydrocarbon, between about 10% andabout 50% by weight crumb rubber, and between about 0.1% and about 50%by weight rheological agent.
 9. The method of claim 8 wherein saidrheological agent comprises a low or non-expansive clay.
 10. The methodof claim 8 wherein said crumb rubber comprises particles of reclaimedrubber, at least a portion of which pass through a #10 mesh U.S. seriessieve.
 11. The method of claim 8 wherein said crumb rubber comprisesparticles of reclaimed rubber, at least a portion of which pass througha #200 mesh U.S. series sieve.
 12. The method of claim 8 wherein saidaromatic petroleum hydrocarbon is polymer modified and contains up toabout 20%, by weight, synthetic polymer.
 13. The method of claim 8wherein said crumb rubber is mixed with said aqueous emulsion atsubstantially ambient temperature.
 14. The method of claim 8 whereinsaid crumb rubber is mixed with said aqueous emulsion at a temperaturebelow the boiling point of said aqueous emulsion.
 15. A method oftreating a recycled asphalt pavement comprising mixing particles ofrecycled asphalt pavement with an additive composition preparedaccording to claim
 1. 16. A method of treating a recycled asphaltpavement comprising mixing particles of recycled asphalt pavement withan additive composition prepared according to claim
 8. 17. A compositionprepared according to the method of claim
 1. 18. A composition preparedaccording to the method of claim 8.